# Optical Second-harmonic Images of Sacran Megamolecule Aggregates

## TL;DR

This study demonstrates the use of optical second harmonic generation microscopy to visualize and analyze the molecular aggregation and orientation of sacran megamolecules in various forms, revealing diverse aggregation behaviors.

## Contribution

First application of SHG microscopy to image and analyze sacran megamolecular aggregates and their molecular orientations.

## Key findings

- SHG signals detected from sacran aggregates and films.
- SHG intensity varies with polarization, indicating molecular orientation.
- Distinct aggregation patterns observed in different sacran forms.

## Abstract

We have detected a second-order nonlinear optical response from aggregates of the ampholytic megamolecular polysaccharide sacran extracted from cyanobacterial biomaterials, by using optical second harmonic generation (SHG) microscopy. The SHG images of sacran cotton-like lump, fibers, and cast films showed SHG intensity microspots of several tens of micrometers in size. The dependence of the SHG spot intensity on an excitation light polarization angle was observed to illustrate sacran molecular orientation in these microdomains. We also observed SHG signals around a special region of the cast film edges of sacran. These results show that sacran megamolecules aggregate in several different ways.